Gel reduction in blends of thermoplastic polyurethane and hydroxyl functional polymers

ABSTRACT

Gas barrier layers and composites contain a low gel sheet produced from a composition containing a thermoplastic polyurethane (TPU), a hydroxyl functional copolymer, and a gel reducing additive. The gel reducing additive has functional groups that can react with isocyanate groups to reduce gel formation during the processing of blends of urethane containing polymers and hydroxyl functional polymers. Multilayer composites containing the low gel sheets can be made into inflatable membranes for containing an inflationary gas. In a particularly preferred embodiment, the membranes are used as bladders of cushioning devices in the soles of shoes, particularly athletic shoes.

FIELD OF THE INVENTION

The present invention relates to composite materials used as gas barrierlayers. More particularly, the invention relates blends of thermoplasticpolyurethane and hydroxyl functional gas barrier copolymers, and tomethods of reducing gel during their preparation.

BACKGROUND OF THE INVENTION

Polymer films made of certain hydroxyl functional copolymers are wellknown for their gas barrier properties. For example, a copolymer ofethylene and vinyl alcohol may be extruded into a film that is resistantto the flow of gases such as oxygen. Such films find use in, forexample, the food packaging industry to prevent spoilage of perishableproduce.

The gas barrier material may also be used to form a pressurized bladderor cushioning device for applications such as in footwear. In thisapplication, the gas barrier layer may be alternated in the membranewith a second layer made of an elastomeric material. Bonk et al. in U.S.Pat. No. 6,127,026 describe such a membrane comprising a microlayerpolymeric composite having at least about 10 microlayers. Themicrolayers alternate between at least one gas barrier material and atleast one elastomeric material, exemplified by thermoplasticpolyurethane (TPU).

To conserve natural resources, it is desirable to recycle and reusecomposites containing such barrier layers and elastomeric materials. Forexample, to recycle the composite of Bonk et al. U.S. Pat. No.6,127,026, it is possible to grind the composite to obtain a mixturecontaining both the gas barrier layer material and the thermoplasticpolyurethane.

In addition, it is known to use blends of TPU and copolymers of ethyleneand vinyl alcohol (EVOH) to produce coextruded sheets for a variety ofuses related to gas barriers. For example, Bonk et al in U.S. Pat. No.6,203,868 describe membranes including a barrier layer made of a blendof one or more thermoplastic polyurethanes and one or more copolymers ofethylene and vinyl alcohol.

Making blends of TPU and EVOH may involve regrinding composites such asdescribed above or coextruding blends of thermoplastic polyurethane andbarrier polymer at elevated temperature. When such components are groundand coextruded, a gel is observed to form in the mixture thatdeleteriously affects flow properties, handleability, and appearance ofthe extruded layer. In particular, the formation of gel leads to a hazyappearance in the coextruded layer. For cosmetic purposes, and toimprove the handleability of coextruded blends of thermoplasticpolyurethane and hydroxyl functional polymers such as ethylene vinylalcohol copolymer, it would be desirable to reduce the gel content ofthe coextruded sheets prepared from the blend of TPU and hydroxylfunctional polymer.

SUMMARY OF THE INVENTION

Improved gas barrier layers and composites are produced according to theinvention by forming a low gel sheet from a composition containing threecomponents. A first component comprises a thermoplastic polyurethane(TPU). A second component comprises a hydroxyl functional copolymer, andthe third component is a gel reducing additive. In another aspect, apolymer composition with decreased gel forming tendency when blendedwith polymers containing urethane linkages is provided. The compositioncontains a hydroxyl functional polymer as described above and the gelreducing additive. Upon adding a urethane polymer such as athermoplastic polyurethane to the polymer composition, a composition isobtained that can be formed or extruded into a sheet having desirableproperties.

In another embodiment, sheets made from the compositions are provided.The sheets are produced by combining the first, second, and thirdcomponents to form a blend, applying thermal energy, mechanical energyor both to the blend, and producing a sheet from the blend.

In another embodiment, a multilayer composite is provided made up of aplurality of flexible layers. At least one of the flexible layers is theproduct of forming a sheet from a blend of thermoplastic polyurethane,hydroxyl functional copolymer, and gel reducing additives as describedabove. In a preferred embodiment, the multilayer composite containsalternating layers of thermoplastic polyurethane and hydroxyl functionalpolymer, for example ethylene vinyl alcohol copolymer (EVOH). Inaddition, at least one of the flexible layers is produced from a blendof thermoplastic polyurethane and hydroxyl functional copolymer, formedfor example by coextrusion in the presence of the gel reducing additive.

In a preferred embodiment, the multilayer composite can be made into aninflatable membrane for containing an inflationary gas. The membrane ismade of a multilayer composite, wherein the composite contains at leastone flexible layer made of a blend of thermoplastic polyurethane,hydroxyl functional copolymer, and a gel reducing additive as describedabove. In a particularly preferred embodiment, the membranes are used asbladders of cushioning devices in the soles of shoes, particularlyathletic shoes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a side elevational view of an athletic shoe in accordance withthe present invention with a portion of the mid-sole cut-a-way to exposea cross-sectional view;

FIG. 2 is a bottom elevational view of the athletic shoe of FIG. 1 witha portion cut-a-way to expose another cross-sectional view;

FIG. 3 is a section view taken alone line 3-3 of FIG. 1;

FIG. 4 is a fragmentary side perspective view of one embodiment of atubular-shaped, two-layer cushioning device in accordance with thepresent invention;

FIG. 5 is a sectional view taken along line 4-4 of FIG. 4;

FIG. 6 is a fragmentary side perspective view of a second embodiment ofa tubular-shaped, three-layer cushioning device in accordance with thepresent invention; and

FIG. 7 is a sectional side view taken along line 6-6 of FIG. 6;

FIG. 8 is a schematic illustration of multilayer composites of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A polymer composition, which has a decreased gel forming tendency whenblended with polymers containing urethane linkages, contains a hydroxylfunctional barrier copolymer and a gel reducing additive. The polymercomposition may be added to a urethane-containing polymer such asthermoplastic polyurethane to provide low gel compositions of theinvention. The low gel compositions may be extruded or otherwise formedinto sheets. The sheets may be used to provide multilayer composites,gas barrier membranes, and other devices of the invention.

The gel reducing additive of the compositions preferably has molecularweight less than the molecular weight of the hydroxyl functionalcopolymer, further defined below. The gel reducing additive furthercomprises one or more functional groups capable of reacting with theurethane linkages of the thermoplastic polyurethane of the composition.In a preferred embodiment, the gel reducing additive is selected fromthe group consisting of compounds with at least one hydroxyl group,compounds with at least one primary amino group, compounds with at leastone secondary amino group, compounds with at least one carboxyl group,and compounds with at least one carboxylic anhydride group. It isbelieved that the gel reducing additive functions to reduce gel in theblends of thermoplastic polyurethane and hydroxyl functional polymer bycompeting with the hydroxyl functional polymer for reaction with theurethane linkages of the thermoplastic polyurethane. In one embodiment,it is preferred to use a gel reducing additive having at least oneprimary hydroxyl group.

It is believed that the gel is formed through a series of chemicalreactions between TPU and the hydroxyl functional copolymer. The firststep is dissociation of urethane linkage in TPU to form an isocyanateand a hydroxyl group. The newly generated isocyanate group subsequentlyreacts with a hydroxyl group of EVOH or other hydroxyl functionalcopolymers to form a new urethane linkage. Since an EVOH chain containsmultiple hydroxyl groups, several polyurethane molecules can be attachedto the same EVOH chain and two or more EVOH chains can join togetherthrough polyurethane segments to form a network or gel. The gel reducingadditive is believed to reduce gel by reacting preferentially withregenerated isocyanate groups formed during the dissociation process. Toensure that the regenerated isocyanate groups are consumedpreferentially by the gel reducing additive, the gel reducing additiveshould preferably contain functional groups more reactive to isocyanatethan the hydroxyl groups of the hydroxyl functional copolymers. When thehydroxyl functional copolymer contains secondary hydroxyl groups (suchas is the case with EVOH), the gel reducing agent may contain primaryalcohols or amine groups that tend to react faster with isocyanate thando secondary hydroxyls. When the hydroxyl functional copolymer containsprimary hydroxyl groups or a mixture of secondary and primary hydroxylgroups, it is to be expected that a slightly higher concentration of gelreducing additive may be needed to effectively “compete” with therelatively more reactive primary hydroxyls of the copolymer. In apreferred embodiment, the gel reducing additive has a lower molecularweight than the copolymer, so that any reaction product with the TPUwill tend not to lead to gel formation. The gel reducing additive mayalso have carboxyl or anhydride functional groups. In a preferredembodiment, the gel reducing additive should also have solubility andmobility in the thermoplastic polyurethane to increase the rate ofreaction. In one aspect, low molecular weight additives are preferredfor their high solubility and rapid diffusion in the thermoplastic, aswell as the high hydroxyl to mass ratio.

In a preferred embodiment, the gel reducing additive comprises apolyester polyol, preferably a polyester diol. The polyester polyols arein general prepared by the condensation polymerization of polyacidcompounds and polyol compounds. Preferably, the polyacid compounds andpolyol compounds are di-functional. Diacid compounds and diols may beused to prepare substantially linear polyester diols, although minoramounts of tri-functional and higher functionality materials (forexample up to about 5 mole percent) can be included. Suitable acidcompounds include, without limitation, glutaric acid, succinic acid,malonic acid, oxalic acid, phthalic acid, isophthalic acid, terephthalicacid, cyclohexanedicarboxylic acid, hexahydrophthalic acid, adipic acid,and maleic acid, as well as esters of these. Mixtures of diacidcomponents may also be used. Suitable polyols include, withoutlimitation, ethylene glycol, diethylene glycol, triethylene glycol,tetra-ethylene glycol, propylene glycol, dipropylene glycol,tripropylene glycol, tetrapropylene glycol, cyclohexanedimethanol,2-ethyl-1,6-hexanediol, Esterdiol 204 (sold by Eastman Chemical Co.),1,4-butanediol, 1,5-pentanediol, 1,3-propanediol, butylene glycol, andneopentyl glycol. Combinations of polyols may also be used. Smallamounts of triols or higher functionality polyols, such astrimethylolpropane or pentaerythritol, are sometimes included. In apreferred embodiment, the carboxylic acid includes adipic acid and thediol includes 1,4-butanediol. Typical catalysts for the esterificationpolymerization are protonic acids, Lewis acids, titanium alkoxides, anddialkyltin oxides.

In another embodiment, the gel reducing additive comprises a polyetherpolyol, preferably a polyether diol. Polyether polyols and diols may besynthesized by reacting a hydroxyl functional initiator with a cyclicether compound to produce the polyether polyol or diol. The cyclic etheris preferably selected from the group consisting of ethylene oxide,propylene oxide, butylene oxide, tetrahydrofuran, and combinations ofthese. The polymerization may be carried out, for example, by chargingthe hydroxyl functional initiator and a catalytic amount of caustic,such as potassium hydroxide, sodium methoxide, or potassiumtert-butoxide, and adding the alkylene oxide at a sufficient rate tokeep the monomer available for reaction. Two or more alkylene oxidemonomers may be randomly copolymerized by coincidental addition orpolymerized in blocks by sequential addition. Alkylene oxide polymersegments produced by such copolymerization include without limitation,the polymerization products of ethylene oxide, propylene oxide,cyclohexene oxide, 1-butene oxide, 2-butene oxide, 1-hexene oxide,tert-butylethylene oxide, phenyl glycidyl ether, 1-decene oxide,isobutylene oxide, cyclopentene oxide, 1-pentene oxide, andcombinations.

In a preferred embodiment, the polyester polyol and the polyether polyolused as gel reducing additives have a number average molecular of weightfrom about 300 to about 4000, more preferably from about 400 to 3000,and more preferably from about 500 to about 2000. In another embodiment,a polyester polyol or polyether polyol is used having a number averagemolecular weight of about 2000 or less, preferably about 1000 or less.

In addition to the polymeric polyester polyol and polyether polyoldescribed above, the gel reducing additive may also be monomeric. In apreferred embodiment, the molecular weight of the gel reducing additiveis less than or equal about 400, and preferably less than or equal toabout 200. It is preferred to use a gel reducing additive having two ormore hydroxyl groups, or having two or more amino groups. Non-limitingexample of gel reducing additives include hydroxyl-functional additivessuch as ethylene glycol, diethylene glycol, cyclohexanedimethanol,glycerol, trimethylolpropane, ditrimethylolpropane, pentaerythritol,polyethylene glycol of molecular weight less than or equal to 400,propylene glycol, and dipropylene glycol, and amine functional additivessuch ethylenediamine, diethylenetriamine, triethylenetetramine, aniline,benzylamine, anisidine, toluidine, aminophenol, aminoacetanilide, and1-(2-aminoethyl)piperazine.

The hydroxyl functional copolymer components of the compositions of theinvention are preferably selected from copolymers known to have gasbarrier properties. In general, they comprise a polymer having 10 molepercent or more of repeating units of structure

wherein n is 0 or 1, R₁ and R₂ are independently hydrogen, methyl, orethyl, and R₃ is hydrogen or C₁₋₃ alkyl. Preferably, the hydroxylfunctional copolymer contains 30 mole percent or more repeating units ofthe above structure. In other preferred embodiments, the hydroxylfunctional copolymer contains at least 45 mole percent, at least 55 molepercent, and at least 65 mole percent repeating units of the abovestructure.

The polymer may contain more than one kind of repeating unit of theabove-mentioned structure having the same or different R₁, R₂, R₃, andn. Where the polymer contains more than one kind of repeating unit, themole percent content of the structural units is given as its totalamount.

In addition to the repeating units of the above-mentioned structure, thepolymer may contain co-monomers in an amount such that acceptableperformance of the gas barrier material is maintained. Examples of theco-monomer include olefin monomers such as ethylene, propylene,1-butene, isobutene, 1-pentene, 1-hexene, and 1-octene; diene monomerssuch as butadiene and isoprene; aromatic substituted vinyl monomers suchas styrene and a-methylstyrene; acrylate monomers such as methylacrylate, ethyl acrylate, butyl acrylate and methyl methacrylate; vinylether monomers such as methyl vinyl ether, ethyl vinyl ether, and butylvinyl ether; vinyl halide monomers such as vinyl chloride and vinylfluoride; vinylidene halide monomers such as vinylidene chloride andvinylidene fluoride; acrylonitrile monomers such as acrylonitrile andmethacrylonitrile; and maleic acid derivatives such as maleimide,N-methylmaleimide, and dimethylmaleimide.

In the case where the polymer contains comonomers, the monomers may bearranged in random, alternating, or block fashion.

The repeating units of the above structure may be incorporated into thepolymers and copolymers by a number of known methods. In a firstexample, an acrylate or methacrylate monomer may be polymerized,followed by reduction to the hydroxyl containing compound. In a secondmethod, the hydroxyl containing repeating units may be incorporated bypolymerization of unsaturated alcohols such as allyl alcohol ormethallyl alcohol. In a third method, the hydroxyl containing repeatingunit may be incorporated by polymerizing an allyl halide derivative,followed by conversion of the halogen into a hydroxyl group. Suchmethods of synthesis are known in the art, and are described for examplein Ikeda et al. U.S. Pat. No. 6,096,393 and references cited therein.The copolymers may also be prepared by polymerizing vinyl estermonomers, such as vinyl acetate followed by a saponification step toremove the ester group and provide a vinyl hydroxide functional group.

A preferred hydroxyl functional copolymer is a copolymer of ethylene andvinyl alcohol (EVOH). Such polymers may be conveniently obtained bypreparing a saponification product of an ethylene vinyl acetatecopolymer. In a preferred embodiment, the content of ethylene is 20 molepercent or greater, preferably from 20-60 mole percent, and morepreferably from 20-55 mole percent. In another embodiment, the contentof ethylene units of EVOH is preferably 10-99 mole percent, morepreferably 20-75 mole percent, and more preferably 25-60 mole percent,particularly 25-50 mole percent. The saponification degree of the vinylester units is preferably at least 50 mole percent, more preferably atleast 90 mole percent. In a preferred embodiment, the saponificationdegree is at least 95 mole percent and more preferably at least 98 molepercent.

Commercially available EVOH include SOARNOL™, from Nippon Gohsei Co.,Ltd. (U.S.A.) of New York, N.Y., and EVAL®, from Eval Company ofHouston, Tex. For example, EVAL® LCF101A has an average ethylene contentof between about 25 mol % and about 48 mol %. In general, lower ethylenecontents result in stronger bonding between the respective layers ofthermoplastic urethane and ethylene-vinyl alcohol copolymers.

As the thermoplastic polyurethane of the invention, particularlysuitable are thermoplastic polyester-polyurethanes,polyether-polyurethanes, and polycarbonate-polyurethanes, including,without limitation, polyurethanes polymerized using as diol reactantspolytetrahydrofurans, polyesters, polycaprolactone polyesters, andpolyethers of ethylene oxide, propylene oxide, and copolymers includingethylene oxide and propylene oxide. These polymeric diol-basedpolyurethanes are prepared by reaction of the polymeric diol (polyesterdiol, polyether diol, polycaprolactone diol, polytetrahydrofuran diol,or polycarbonate diol), one or more polyisocyanates, and, optionally,one or more chain extension compounds. Chain extension compounds, as theterm is used herein, are compounds having two or more functional groupsreactive with isocyanate groups. Preferably the polymeric diol-basedpolyurethane is substantially linear (i.e., substantially all of thereactants are di-functional).

The polyester diols used in forming the preferred thermoplasticpolyurethane of the invention are in general prepared by thecondensation polymerization of polyacid compounds and polyol compounds.Preferably, the polyacid compounds and polyol compounds aredi-functional, i.e., diacid compounds and diols are used to preparesubstantially linear polyester diols, although minor amounts ofmono-functional, tri-functional, and higher functionality materials(perhaps up to 5 mole percent) can be included. Suitable dicarboxylicacids include, without limitation, glutaric acid, succinic acid, malonicacid, oxalic acid, phthalic acid, hexahydrophthalic acid, adipic acid,maleic acid and mixtures of these. Suitable polyols include, withoutlimitation, wherein the extender is selected from the group consistingof ethylene glycol, diethylene glycol, triethylene glycol, tetraethyleneglycol, propylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol, cyclohexanedimethanol, 2-ethyl-1,6-hexanediol,Esterdiol 204 (sold by Eastman Chemical Co.), 1,4-butanediol,1,5-pentanediol, 1,3-propanediol, butylene glycol, neopentyl glycol, andcombinations thereof. Small amounts of triols or higher functionalitypolyols, such as trimethylolpropane or pentaerythritol, are sometimesincluded. In a preferred embodiment, the carboxylic acid includes adipicacid and the diol includes 1,4-butanediol. Typical catalysts for theesterification polymerization are protonic acids, Lewis acids, titaniumalkoxides, and dialkyltin oxides.

The polymeric polyether or polycaprolactone diol reactant used inpreparing the preferred thermoplastic polyurethanes is prepared byreacting a diol initiator, e.g., ethylene or propylene glycol, with alactone or alkylene oxide chain-extension reagent. Preferredchain-extension reagents are epsilon caprolactone, ethylene oxide, andpropylene oxide. Lactones that can be ring opened by an active hydrogenare well-known in the art. Examples of suitable lactones include,without limitation, ε-caprolactone, γ-caprolactone, β-butyrolactone,β-propiolactone, γ-butyrolactone, α-methyl-γ-butyrolactone,β-methyl-γ-butyrolactone, γ-valerolactone, δ-valerolactone,γ-decanolactone, δ-decanolactone, γ-nonanoic lactone, γ-octanoiclactone, and combinations of these. In one preferred embodiment, thelactone is ε-caprolactone. Lactones useful in the practice of theinvention can also be characterized by the formula:

wherein n is a positive integer of 1 to 7 and R is one or more H atoms,or substituted or unsubstituted alkyl groups of 1-7 carbon atoms. Usefulcatalysts include those mentioned above for polyester synthesis.Alternatively, the reaction can be initiated by forming a sodium salt ofthe hydroxyl group on the molecules that will react with the lactonering.

In another embodiment of the invention, a diol initiator is reacted withan oxirane-containing compound to produce a polyether diol to be used inthe polyurethane polymerization. The oxirane-containing compound ispreferably an alkylene oxide or cyclic ether, especially preferably acompound selected from ethylene oxide, propylene oxide, butylene oxide,tetrahydrofuran, and combinations of these. Alkylene oxide polymersegments include, without limitation, the polymerization products ofethylene oxide, propylene oxide, 1,2-cyclohexene oxide, 1-butene oxide,2-butene oxide, 1-hexene oxide, tert-butylethylene oxide, phenylglycidyl ether, 1-decene oxide, isobutylene oxide, cyclopentene oxide,1-pentene oxide, and combinations of these. The alkylene oxidepolymerization is typically base-catalyzed. The polymerization may becarried out, for example, by charging the hydroxyl-functional initiatorand a catalytic amount of caustic, such as potassium hydroxide, sodiummethoxide, or potassium tert-butoxide, and adding the alkylene oxide ata sufficient rate to keep the monomer available for reaction. Two ormore different alkylene oxide monomers may be randomly copolymerized bycoincidental addition and polymerized in blocks by sequential addition.Homopolymers or copolymers of ethylene oxide or propylene oxide arepreferred.

Tetrahydrofuran polymerizes under known conditions to form repeatingunits of —[CH₂CH₂CH₂CH₂O]—. Tetrahydrofuran is polymerized by a cationicring opening reaction using such counterions as SbF₆ ⁻, AsF₆ ⁻PF₆ ⁻,SbCl₆ ⁻, BF₄ ⁻, CF₃SO₃ ⁻, FSO₃ ⁻, and ClO₄ ⁻. Initiation is by formationof a tertiary oxonium ion. The polytetrahydrofuran segment can beprepared as a “living polymer” and terminated by reaction with thehydroxyl group of a diol such as any of those mentioned above.

Aliphatic polycarbonate diols are prepared by the reaction of diols withdialkyl carbonates (such as diethyl carbonate), diphenyl carbonate, ordioxolanones (such as cyclic carbonates having five- and six-memberrings) in the presence of catalysts like alkali metal, tin catalysts, ortitanium compounds. Useful diols include, without limitation, any ofthose already mentioned. Aromatic polycarbonates are usually preparedfrom reaction of bisphenols, e.g., bisphenol A, with phosgene ordiphenyl carbonate.

The polymeric diol, such as the polymeric polyester diols describedabove, which are used in the polyurethane synthesis preferably have anumber average molecular weight (determined for example by the ASTMD-4274 method) of from about 300 to about 4,000; more preferably fromabout 400 to about 3,000; and still more preferably from about 500 toabout 2,000. The polymeric diol generally forms a “soft segment” of theelastomeric polyurethane.

The synthesis of the elastomeric polyurethane may be carried out byreacting one or more of the above polymeric diols, one or more compoundshaving at least two isocyanate groups, and, optionally, one or morechain extension agents. The elastomeric polyurethanes are preferablylinear and thus the polyisocyanate component preferably is substantiallydi-functional. Useful diisocyanate compounds used to prepare thethermoplastic polyurethanes of the invention include, withoutlimitation, isophorone diisocyanate (IPDI), methylene bis-4-cyclohexylisocyanate (H₁₂MDI), cyclohexane diisocyanate (CHDI), m-tetramethylxylene diisocyanate (m-TMXDI), p-tetramethyl xylene diisocyanate(p-TMXDI), ethylene diisocyanate, 1,2-diisocyanatopropane,1,3-diisocyanatopropane, 1,6-diisocyanatohexane (hexamethylenediisocyanate or HDI), 1,4-butylene diisocyanate, lysine diisocyanate,1,4-methylene bis(cyclohexyl isocyanate), the various isomers of toluenediisocyanate, meta-xylylenediisocyanate and para-xylylenediisocyanate,4-chloro-1,3-phenylene diisocyanate, 1,5-tetrahydronaphthalenediisocyanate, 4,4′-dibenzyl diisocyanate, 1,2,4-benzene triisocyanate,xylylene diisocyanate (XDI), and combinations thereof. Particularlyuseful is diphenylmethane diisocyanate (MDI).

Useful active hydrogen-containing chain extension agents generallycontain at least two active hydrogen groups, for example, diols,dithiols, diamines, or compounds having a mixture of hydroxyl, thiol,and amine groups, such as alkanolamines, aminoalkyl mercaptans, andhydroxyalkyl mercaptans, among others. The molecular weight of the chainextenders preferably range from about 60 to about 400. Alcohols andamines are preferred. Typical examples of useful diols that are used aspolyurethane chain extenders include, without limitation,1,6-hexanediol, cyclohexanedimethanol (sold as CHDM by Eastman ChemicalCo.), 2-ethyl-1,6-hexanediol, Esterdiol 204 (sold by Eastman ChemicalCo.), 1,4-butanediol, ethylene glycol and lower oligomers of ethyleneglycol including diethylene glycol, triethylene glycol and tetraethyleneglycol; propylene glycol and lower oligomers of propylene glycolincluding dipropylene glycol, tripropylene glycol and tetrapropyleneglycol; 1,3-propanediol, 1,4-butanediol, neopentyl glycol,dihydroxyalkylated aromatic compounds such as the bis (2-hydroxyethyl)ethers of hydroquinone and resorcinol; p-xylene-α, α′-diol; the bis(2-hydroxyethyl) ether of p-xylene-α, α′-diol; m-xylene-α, α′-diol,their bis(2-hydroxyethyl) ethers and mixtures thereof. Suitable diamineextenders include, without limitation, p-phenylenediamine,m-phenylenediamine, benzidine, 4,4′-methylenedianiline,4,4′-methylenebis(2-chloroaniline), ethylene diamine, and combinationsof these. Other typical chain extenders are amino alcohols such asethanolamine, propanolamine, butanolamine, and combinations of these.Preferred extenders include ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, dipropyleneglycol, tripropylene glycol, tetrapropylene glycol, 1,3-propyleneglycol, 1,4-butanediol, 1,6-hexanediol, and combinations of these.

In addition to the above-described difunctional extenders, a smallamount of trifunctional extenders such as trimethylolpropane,1,2,6-hexanetriol and glycerol, and/or monofunctional active hydrogencompounds such as butanol or dimethyl amine, may also be present. Theamount of trifunctional extenders and/or monofunctional compoundsemployed would preferably be 5.0 equivalent percent or less based on thetotal weight of the reaction product and active hydrogen containinggroups employed.

The reaction of the polyisocyanate, polymeric diol, and chain extensionagent is typically conducted by heating the components, for example bymelt reaction in a twin screw extruder. Typical catalysts for thisreaction include organotin catalysts such as stannous octoate.Generally, the ratio of polymeric diol, such as polyester diol, toextender can be varied within a relatively wide range depending largelyon the desired hardness of the final polyurethane elastomer. Forexample, the equivalent proportion of polyester diol to extender may bewithin the range of 1:0 to 1:12 and, more preferably, from 1:1 to 1:8.Preferably, the diisocyanate(s) employed are proportioned such that theoverall ratio of equivalents of isocyanate to equivalents of activehydrogen containing materials is within the range of 0.95:1 to 1.10:1,and more preferably, 0.98:1 to 1.04:1. The polymeric diol segmentstypically are from about 35% to about 65% by weight of the polyurethanepolymer, and preferably from about 35% to about 50% by weight of thepolyurethane polymer.

It may be desirable under certain applications to include blends ofpolyurethanes to form the structural layers of the polymeric compositesof the invention, such as when susceptibility to hydrolysis is ofparticular concern. For example, a polyurethane including soft segmentsof polyether diols or polyester diols formed from the reaction mixtureof a carboxylic acid and a diol wherein the repeating units of thereaction product has more than eight carbon atoms can be blended withpolyurethanes including polyester diols having repeating units of eightor less carbon atoms or products of branched diols. Preferably, thepolyurethanes other than those including polyester diol repeating unitshaving eight or less carbon atoms or with oxygen atoms connected totertiary carbons will be present in the blends in an amount up to about30 wt. %, (e.g. 70 wt. % polyethylene glycol adipate based polyurethane,30% isophthalate polyester diol based polyurethane). Specific examplesof the polyester diols wherein the reaction product has more than eightcarbon atoms include poly(ethylene glycol isophthalate),poly(1,4-butanediol isophthalate) and poly(1,6-hexanediol isophthalate).

As an alternative to blends of various thermoplastic polyurethanes, asingle polyurethane having various soft segments may be used. Again,without intending to be limiting, the soft segments may include, inaddition to soft segments having a total of eight carbon atoms or less,polyether diols, polyester diols having a total of more than eightcarbon atoms, or mixtures thereof. It is contemplated that the totalamount of soft segment constituency which includes the reaction productof a carboxylic acid and a diol having a total carbon atom count of morethan eight, be present in an amount of up to about 30 wt. % of the totalweight of soft segments included in the polyurethane. Thus, at least 70wt. % of the soft segment repeating units will be the reaction productsof carboxylic acid and a diol, wherein the total carbon atom count forthe reaction product is eight or less.

It should also be noted that there are a number of ways to addpolyurethanes with up to 30 wt. % of polyesters with repeat unitscontaining more than eight carbon atoms to the polyurethanes of thisinvention. Thirty percent or less of a polyurethane derived frompolyester diols containing repeat units with more than eight carbons canbe blended as finished polymers with 70 wt. % or more of polyurethanesderived from polyester diols with repeat units containing eight or lesscarbon atoms, or a single polyurethane could be prepared from a mixtureof polyester diols wherein 70 wt. % or more contain repeat units witheight carbons or less and the balance contains repeat units with morethan eight carbons as described previously. A polyurethane could beprepared from a single diol prepared by reaction from dicarboxylic acidsand diols such that 70 wt. % of the repeat units in the polyester diolcontain eight or less carbon atoms. Combinations of these techniques arealso possible. Among the acids that contain more than six carbon atomsthat could be employed are isophthalic and phthalic acids.

The compositions containing thermoplastic urethane, hydroxyl functionalcopolymer, and gel reducing additive may be used in a process forpreparing a sheet comprising a blend of thermoplastic polyurethane andat least one hydroxyl functional copolymer. The three components arefirst combined, and then thermal energy, mechanical energy, or both isapplied to the combination to produce a blend. A sheet is then producedfrom the blend, the sheet generally having lower gel content than asheet produced from a composition containing only the thermoplasticpolyurethane and hydroxyl functional copolymer, without the gel reducingadditive.

The three components may be combined in any order. In one embodiment,the three components are added in turn to a mixing chamber. In anotherembodiment, a composition containing the hydroxyl functional copolymerand the gel reducing additive is first prepared by combining the twocomponents. This composition, as discussed above, exhibits a decreasedgel forming tendency when blended with polymers containing urethanelinkages. To form the blend, the two component composition is added to athermoplastic polyurethane.

The gel reducing additive is generally present in the composition inminor amounts—typically up to 20% by weight, and preferably up to about5% by weight—depending on the desired reduction of gel content and themolecular weight of the additive and level of hydroxyl functionalpolymer in the composition. The proportion of TPU and hydroxylfunctional polymer may also vary over a wide range. Generally, thecompositions may contain from 1% by weight to about 99% by weight of thehydroxyl functional barrier copolymer. Higher levels (for example60-98%) may be used for applications requiring high gas barrierproperties, such as the multilayer beverage bottle discussed below. Onthe other hand, relatively lower levels of hydroxyl functional polymer,with concomitantly higher levels of TPU, may be used when it is desiredfor the low gel blend sheet to have more durable structural properties.

To produce the blend, thermal energy, mechanical energy, or both may beapplied to the combination of the three components. Generally, thermalenergy is applied in order to soften or melt the components. Mechanicalenergy may be applied for example in the form of stirring, mixing,milling, or grinding. The mechanical energy applied to the combinationserves to thoroughly mix the three components into a homogenous blend.

A sheet may be produced from the blend by a number of known processesincluding, without limitation, extrusion, casting, and molding. In apreferred embodiment, low gel sheets are produced from the blend byextruding the blend. Alternatively, the low gel sheets can be coextrudedwith other thermoplastic and gas barrier layers as discussed below.

The low gel sheets produced from a combination of thermoplasticpolyurethane, hydroxyl functional barrier polymer, and gel reducingadditive may be used in a variety of applications that take advantage ofthe improved physical properties and gas barrier characteristics of thesheet. Generally, the applications involve the use of a multi-layercomposite comprising a plurality of flexible layers, wherein at leastone of the flexible layers is the product of forming a sheet from ablend of thermoplastic polyurethane, hydroxyl functional copolymer, andgel reducing additive as discussed above. The plurality of flexiblelayers may be made of a variety of materials, including withoutlimitation thermoplastic polyurethane, hydroxyl functional gas barriercopolymer layers, copolymers of ethylene and vinyl alcohol, polyesters,polycarbonates, and polyamides. The low gel sheets may have a variety ofthicknesses, depending on the application.

In one embodiment, a hose is provided having a rubber as outer layer,and a layer made from a blend of thermoplastic polyurethane, hydroxylfunctional copolymer, and a gel reducing additive as inner layer. Thehose exhibits advantageous permeability characteristics to Freon 22 andother gases, and good pressure retention during prolonged use. Forexample, the inner layer may comprise a mixture of 1-95%, preferably30-95% by weight of an ethylene vinyl alcohol copolymer (having 20-60mole % ethylene units), up to 99%, preferably 5-75% by weightthermoplastic polyurethane, and 0.05-5%, preferably 0.1-1.0% by weightgel reducing additives such as glycerin. The outer layer may be madefrom a natural rubber or from a synthetic rubber such as EPDM. Suchhoses having decreased permeability to Freon 22 and other gases aredescribed for example in Japanese patent JP-03255288, assigned toKuraray Co., Ltd. of Japan. They may be prepared by coextrusion of theTPU blend layer and the rubber layer.

In another embodiment, gas barrier impact resistant multi-layercontainers are provided wherein one of the layers is produced from ablend containing thermoplastic polyurethane, hydroxyl functional gasbarrier copolymer, and gel reducing additive. The low gel TPU blendlayers are used along with one or more layers of thermoplasticpolyesters, polyamides, and/or polycarbonates located on one or moresides of the TPU blend layer to provide bottles having useful flavorretaining properties for packaging beverages, foods, or cosmetics. In anon-limiting example, a 60-98:2-40 blend of 20-60:40-80 (mole %)ethylene vinyl alcohol copolymer and thermoplastic polyurethanes istreated with 1-20% by weight of a gel reducing additive such asglycerin. The TPU/EVOH/glycerin are blended and blow-molded withisophthalic modified PET (as inner and outer layers) to give a bottlehaving layer thickness of 190:20:90 microns from inside to outside. Thereduced gel of the TPU/EVOH layer leads to improved clarity, while theTPU/EVOH blend contributes advantageous gas permeabilitycharacteristics. Such bottles may be made according to proceduresdescribed in Japanese patent JP-03175032 assigned to Kuraray Co., Ltd.of Japan, the disclosure of which is incorporated by reference.

In a preferred embodiment, the low gel sheets containing TPU and ahydroxyl functional gas barrier layer copolymer are used as part of apolymer composite membrane that can be formed into inflatable bladdersand the like for applications such as athletic footwear. For example,referring to FIGS. 1-5, a barrier membrane 28 in accordance withteachings of the present invention is provided in the form of acushioning device. As shown, the membrane 28 has a composite structureincluding an inner layer 30 formed from a blend of TPU, hydroxylfunctional copolymer, and gel reducing additive of the invention. Theinner layer allows for controlled diffusion pumping orself-pressurization. The outer layer 32 is formed of a flexibleresilient elastomeric material which preferably is resistant toexpansion beyond a predetermined maximum volume for the membrane whensubjected to gaseous pressure.

The outer layer 32 preferably is formed of a material or combination ofmaterials which offer superior heat sealing properties, flexural fatiguestrength, a suitable modulus of elasticity, tensile and tear strengthand abrasion resistance. Among the available materials which offer thesecharacteristics, it has been found that thermoplastic elastomers of theurethane variety, otherwise referred to herein as thermoplasticurethanes or simply TPU, are highly preferred because of their excellentprocessability.

Non-limiting examples of thermoplastic urethanes useful in forming theouter layer 32 are PELLETHANE™ 2355-85ATP and 2355-95AE (Dow ChemicalCompany of Midland, Mich.), ELASTOLLAN® (BASF Corporation) and ESTANE®(B.F. Goodrich Co.), all of which are either ester or ether based. Stillother thermoplastic urethanes based on polyesters, polyethers,polycaprolactone, and polycarbonate macroglycols can be employed. In oneembodiment, the thermoplastic urethane(s) employed to form the outerlayer 32 are aromatic in nature.

Referring still to FIGS. 1-5, there is shown an athletic shoe, includinga sole structure and a cushioning device as one example of a productemploying a barrier membrane in accordance with the teachings of thepresent invention. The shoe 10 includes a shoe upper 12 to which thesole 14 is attached. The shoe upper 12 can be formed from a variety ofconventional materials including, but not limited to, leathers, vinyls,nylons and other generally woven fibrous materials. Typically, the shoeupper 12 includes reinforcements located around the toe 16, the lacingeyelets 18, the top of the shoe 20 and along the heel area 22. As withmost athletic shoes, the sole 14 extends generally the entire length ofthe shoe 10 from the toe region 20 through the arch region 24 and backto the heel portion 22.

The sole structure 14 includes one or more selectively permeable barriermembranes 28 in accordance with the present invention, which arepreferably disposed in the mid-sole H of the sole structure. By way ofexample, the barrier membranes 28 of the present invention can be formedhaving various geometries such as the plurality of tubular members whichare positioned in a spaced apart, parallel relationship to each otherwithin the heel region 22 of the mid sole 26 as illustrated in FIGS.1-5. The tubular members are sealed to contain an injected captive gas.More specifically, each of the barrier membranes 28 are formed toinclude a barrier layer which permits diffusion of mobile gases butwhich resists or prevents diffusion of the captive gases. Thesepredetermined diffusion properties of the membrane 28 are provided by aninner barrier layer 30 which is disposed along the inner surface of athermoplastic outer layer 32. These two membrane layers may be best seenin FIGS. 4 and 5. As previously noted, the barrier membranes 28 of thepresent invention can be formed in a variety of configurations orshapes. Barrier membrane configurations under the present invention(whether in the form of a tube, an elongated pad or other suchconfiguration), may either be fully or partially encapsulated within themid-sole or out-sole of an article of footwear. The inner layer 30 isformed from a blend of TPU, hydroxyl functional copolymer, and gelreducing additive as described above.

Referring now to FIGS. 6 and 7, an alternative barrier membraneembodiment 28A in the form of an elongated tubular shaped multi-layeredcomponent is illustrated. The modified barrier membrane 28A isessentially the same as the composite structure illustrated in FIGS. 1-5except that a third layer 34 is provided contiguously along the innersurface of the barrier layer 30, such that the barrier layer 30 issandwiched between the outer layer 32 and innermost layer 34. Theinnermost layer 34 is also preferably made from a thermoplastic urethanematerial to add further protection for the barrier layer 30. In additionto the benefits of enhanced protection against degradation of thebarrier layer 30, layer 34 also tends to assist in providing for highquality welds which allow for the three-dimensional shapes of thecushioning devices.

The cushioning devices shown in FIGS. 1-7 may be fabricated frommulti-layered extruded tubes. Lengths of the coextruded tubing rangingfrom one foot to coils of up to 5 feet may be inflated to a desiredinitial inflation pressure ranging from 0 psi ambient to 100 psi,preferably in the range of 5 to 50 psi, with the captive gas preferablybeing nitrogen. Sections of the tubing are RF welded or heat sealed tothe desired lengths. The individual cushioning devices produced are thenseparated by cutting through the welded areas between adjacentcushioning devices. Alternatively, the extruded tubes may be welded orheat sealed before inflation. It should also be noted that thecushioning devices can be fabricated with so-called lay flat extrudedtubing as is known in the art whereby the internal geometry is weldedinto the tube.

As the blended first layer including the one or more polyester polyolbased urethanes and one or more copolymers of ethylene and vinyl alcoholand the second layer including thermoplastic urethane advance to theexit end of the extruder through individual flow channels, once theynear the die-lip exit, the melt streams are combined and arranged toflow together in layers typically moving in laminar flow as they enterthe die body. In one embodiment, the materials are combined at atemperature of between about 300° F. to about 450° F. and a pressure ofat least about 200 psi to obtain optimal wetting for maximum adhesionbetween the contiguous portions of the layers 30, 32 and 34respectively. Again, for multi-layered laminates, it is preferred thatthe polyester polyols and isocyanate moieties utilized in forming thebarrier layer be aliphatic in nature, since aliphatic urethanes havebeen found to be readily processable utilizing conventional sheetextrusion techniques.

The blended barrier layer 30 will generally include about 1 to 97 weight% of polyester polyol based TPU. In some embodiments, TPU will bepresent up to 50 weight %, preferably 1-30 weight % or 5-25 weight %.

For certain embodiments, it may also be useful to include a relativelysmall amount of at least one aromatic or aliphatic thermoplasticpolyurethane in the blended barrier layer 30 as a viscosity modifier.Under those embodiments employing at least one aromatic thermoplasticurethane, the total amount will generally be 3 wt. % or less based on a100 wt. % constituency of the barrier layer. Thus, the composition ofthe blended barrier layer can be summarized as including: (1) up toabout 95 wt. %, preferably 2% to 95% wt. %, of at least one hydroxylfunctional barrier polymer such as a copolymer of ethylene and vinylalcohol; (2) 1 wt. % to about 99 wt. % of an aliphatic or aromatic orthe combination of two thermoplastic urethanes; and (3) about 0.05 toabout 5 weight % gel reducing additive, wherein the total constituencyof the barrier layer is equal to 100 wt. %. The aromatic thermoplasticurethanes are also selected from the group consisting of polyester,polyether, polycaprolactone, polyoxypropylene and polycarbonatemacroglycol based materials and mixtures thereof.

As previously noted, the barrier membranes as disclosed herein can beformed by various processing techniques including but not limited toextrusion, blow molding, injection molding, vacuum molding and heatsealing or RF welding of tubing and sheet extruded film materials.Preferably, the membranes of the present invention are made from filmsformed by co-extruding the outer layer of thermoplastic urethanematerial and the inner layer of the blended polyester polyol basedthermoplastic urethane and copolymer of ethylene and vinyl alcoholtogether to effectively produce multi-layered film materials with theresulting barrier membranes produced from this material. Subsequently,after forming the multi-layered film materials, the film materials areheat sealed or welded by RF welding to form the inflatable barriermembranes which have the characteristics of both high flexibility anddiffusion pumping capabilities.

In the above embodiments, the low gel sheet containing a blend of TPUand hydroxyl functional barrier copolymer is used in composites toprovide gas barrier properties. In other embodiments, the low gel sheetis used along with other layers of barrier copolymer sheets andelastomeric sheets. Multilayer composites such as these may take on avariety of configurations. Non-limiting examples are schematicallyillustrated in FIGS. 8 a, 8 b, and 8 c. In FIG. 8 a, a multilayercomposite 80 is illustrated having two layers of a low gel TPU blendsheet 81 between which are sandwiched 3 layers including two layers ofan elastomeric sheet 83 and one of a hydroxyl functional copolymerbarrier sheet 85. A similar sandwich device is illustrated in FIG. 8 b,except that the multilayer composite contains 2 sheets of a gas barriercopolymer sheet 85 and three sheets of an elastomeric layer 83.Similarly, in FIG. 8 c, a multilayer composite is shown containing threegas barrier polymer sheets 85 and 4 elastomeric sheets 83. In apreferred embodiment, the gas barrier sheets comprise 1 or more hydroxylfunctional copolymers as described above. Also preferably, theelastomeric material is advantageously a thermoplastic polyurethanesheet.

In FIGS. 8 a, 8 b and 8 c, the overall thickness of the one, two, orthree layers of hydroxyl functional copolymer sheet is selected so as toobtain the desired gas permeability. Typically the total thickness ofthe gas barrier sheets in multilayer composites such as illustrated inFIG. 8 a, 8 b and 8 c is on the order of 1 mil (about 25 micrometers),that is from about 0.1 mil to about 10 mil.

The multilayer composites illustrated in the FIGS. 8 may also containother structural layers, not shown, typically provided on the outside oflow gel layers 81 and 82. Typical structural outside layers includeelastomeric materials, such as thermoplastic polyurethane, naturalrubber, and synthetic rubbers. It is also understood that one or more ofthe sandwiched gas barrier copolymer sheets may be made of a low gelblend of TPU and hydroxyl functional copolymer. The relative thicknessesof the layers and the length of the sheets illustrated in FIGS. 8 a, 8 band 8 c are given for clarity, and do not necessarily represent actualpreferred values.

The low gel TPU blend sheets may also be used to produce microlayerpolymeric composites. The microlayer composites contain significantlymore than the three, five, or seven layers the sandwich structuresillustrated in FIG. 8. In a preferred embodiment, the microlayerpolymeric composite of the invention has alternating thin layers offluid barrier material and a structural, elastomeric material sandwichedbetween low gel TPU blend layers. In one embodiment, the microlayerpolymeric composite has at least about 10 layers. Preferably, themicrolayer polymeric composite has at least about 20 layers, morepreferably at least about 30 layers, and still more preferably at leastabout 50 layers. The microlayer polymeric composite can have thousandsof layers, and the skilled artisan will appreciate that the number oflayers will depend upon such factors as the particular materials chosen,thicknesses of each layer, the thickness of the microlayer polymericcomposite, the processing conditions for preparing the multilayers, andthe final application of the composite. The microlayer elastomermembranes preferably has from about 10 to about 1000 layers, morepreferably from about 30 to about 1000 and even more preferably it hasfrom about 50 to about 500 layers.

Also contemplated are microlayer polymeric composites that includelayers of different fluid barrier materials and/or layers of differentelastomeric materials, all of the different layers being arranged inregular repeating order. Other layers in addition to elastomeric layersand fluid barrier layers that alternate along with them in a regular,repeating order may optionally be included.

The average thickness of each individual layer of the fluid barriermaterial in the microlayer composition may be as low as a few nanometersto as high as several mils (about 100 microns) thick. Preferably, theindividual layers have an average thickness of up to about 0.1 mil(about 2.5 microns). Average thicknesses of about 0.0004 mil (about 0.01micron) to about 0.1 mil (about 2.5 microns) are particularlypreferable. For example, the individual barrier material layers can be,on average, about 0.05 mils (about 1.2 microns). The thinner layers ofthe fluid barrier layer material improves the ductility of the bladdermembrane.

The multilayer polymeric composites may be formed by a variety ofmethods. In a preferred method, a microlayer core composed ofalternating TPU and barrier layers is first made and then structurallayers containing mostly TPU with a minor amount of EVOH are added onboth sides of the core. During formation of the microlayer core, TPUserves as both tie layer and protective layer.

In one process, the multilayer polymeric composites of the invention canbe prepared using a two-layer, three-layer, or five-layer feed blockthat directs the layered stream into a static mixer or layer multiplier.The static mixer has multiple mixing elements, preferably at least about5 elements, that increases the number of layers geometrically.

In another method, the multilayer polymeric composites of the inventioncan be prepared by providing a first stream comprising discrete layersof polymeric material. A preferred embodiment of this method isdescribed in detail in Schrenk, et al., U.S. Pat. No. 5,094,793, issuedMar. 10, 1992, which is incorporated herein in its entirety byreference. Briefly, the first stream comprising discrete layers canagain be formed by directing the molten extrudate from extrudersseparately containing the elastomeric material and the fluid barriermaterial into a two-layer, three-layer, or five-layer feed block. Thefirst stream is then divided into a plurality of branch streams, thebranch streams are then redirected or repositioned and individuallysymmetrically expanded and contracted, being finally recombined in anoverlapping relationship to form a second stream with a greater numberof discrete layers. In addition, protective boundary layers may beincorporated according to the method of Ramanathan et al., U.S. Pat. No.5,269,995, issued Dec. 14, 1993, which is incorporated herein in itsentirety by reference. The protective layers are provided by a steam ofmolten thermoplastic material which is supplied to the exterior surfacesof the composite stream to form a protective boundary layer at the wallof the coextrusion apparatus. The protective layer may add specialoptical or physical attributes to the microlayer polymeric compositematerial, such as special coloration, including metallic colorationobtained by including metallic or other flake pigments in the protectiveboundary layer. The protective layers protect the structural and fluidbarrier layers from instability and breakup during the layer formationand multiplication.

Although it is not necessary for all of the layers to be completelayers, that is to extend in the plane of that layer to all edges of thepiece, it is desirable for most layers to be substantially completelayers, that is to extend to the edges of the membrane.

The elastomeric membrane of the invention includes the microlayerpolymeric composite, either as an only layer or as one layer in alaminate construction. The membrane may be of any convenient length andwidth for forming the desired footwear bladder or hydraulic accumulator.The average thickness of the microlayer polymeric composite of themembrane may vary widely, but it may be, for example, from about 3 mils(about 75 microns) to about 200 mils (about 0.5 cm). Preferably, theaverage thickness of the microlayer polymeric composite is at leastabout 50 microns, preferably from about 75 microns to about 0.5 cm, morepreferably from about 125 microns to about 0.5 cm, and particularlypreferably from about 125 microns to about 0.15 cm. When the microlayerpolymeric composite is to be used to prepare a bladder for footwear itis preferred that the microlayer material have an average thickness offrom about 3 mils (about 75 microns) to about 40 mils (about 0.1 cm),while membranes used in hydropneumatic accumulators are usually thicker.In one preferred embodiment the microlayer polymeric composite has anaverage thickness of at least about 125 microns.

The membrane of the invention can be a laminate that includes themicrolayer polymeric material as one or more laminate layers.Preferably, the alternate layers are selected from the polymers listedabove as suitable as the structural material of the microlayer material,and more preferably the alternate layers are polyurethane materials. Anynumber of microlayer layers, preferably from one to about 5, morepreferably one to three are used as alternate layers of the laminate.The other layers of the laminate preferably as elastomeric and includethermoplastic elastomers selected from those already mentioned assuitable for the structural layers of the microlayer polymericcomposite. One preferred membrane of the invention is a laminate thatincludes at least one layer A of an elastomeric polyurethane and atleast one layer B of the microlayer polymeric composite. In otherpreferred embodiment, the membrane is a laminate having layers A-B-A orlayers A-B-A-B-A.

When the microlayer polymeric film is used to prepare a laminate, thelaminate may have an average thickness of from about 3 mils (about 75microns) to about 200 mils (about 0.5 cm), and preferably it has anaverage thickness of from about 3 mils (about 75 microns) to about 50mils (about 0.13 cm). The microlayer polymeric film layer of thelaminate is preferably from about 0.25 mil (about 6.35 microns) to about102 mils (2600 microns).

A bladder may be produced by RF (radio frequency) welding two sheets ofthe microlayer material or microlayer-containing laminate, particularlywhen one layer is a polar material such as a polyurethane. Non-polarmaterials such as polyolefins can be welded using ultrasound or heatsealing techniques. Other well-known welding techniques may also beemployed.

When used as cushioning devices in footwear such as shoes, the bladdermay be inflated, preferably with nitrogen, to an internal pressure of atleast about 3 psi and up to about 50 psi. Preferably the bladder isinflated to an internal pressure of from about 5 psi to about 35 psi,more preferably from about 5 psi to about 30 psi, still more preferablyfrom about 10 psi to about 30 psi, and yet more preferably from about 15psi to about 25 psi. It will be appreciated by the skilled artisan thatin applications other than footwear applications the desired andpreferred pressure ranges may vary dramatically and can be determined bythose skilled in that particular field of application. Accumulatorpressures, for example, can range up to perhaps 1000 psi.

Preferably, the membranes described herein may be useful for formingcushioning components for footwear. In such applications, the membranespreferably are capable of containing a captive gas for a relatively longperiod of time. In a highly preferred embodiment, for example, themembrane should not lose more than about 20% of the initial inflated gaspressure over a period of approximately two years. In other words,products inflated initially to a steady state pressure of between 20.0to 22.0 psi should retain pressure in the range of about 16.0 to 18.0psi for at least about two years.

The inflationary gas transmission rate of the material for theinflationary gas, which is preferably nitrogen gas, should be less than10 cubic centimeters per square meter per atmosphere per day (cc/m² atmday), preferably less than about 3 cc/m² atm.day, and particularlypreferably less than about 2 cc/m² atm day.

The microlayer polymeric composites provide increased resistance todelamination and cracking. Dividing the barrier layer into numerouslayers increases the resistance of individual layers to cracking. Whilenot wishing to be bound by theory, it is believed that, given the sameexternal dimensions and a constant density of flaws, a laminate withthinner layers will likely contain fewer flaws in each layer. Thus, themicrolayer polymeric composites containing the same amount of barriermaterial overall as a traditional laminate, but having the barriermaterial divided between many more layers than the one layer or fewlayers in the traditional laminate, will contain more barrier materialin uncracked layers than would the traditional laminate if a crackshould develop from each flaw as the material is loaded. In addition, ifa barrier layer in a microlayer composite develops a crack, dissipativeprocesses along the interfaces help to confine the crack to one layer.Fluid transmission rate should not be affected significantly if cracksdevelop within some of the barrier layers because adjacent barrierlayers still force the diffusing species to take a circuitous path inorder to permeate the membrane.

EXAMPLES

In the Examples that follow:

TPU-1 is a butanediol adipate MDI based TPU with a melt index of about12 and a shore A hardness of 80A.

TPU-2 is Kuramiron® U #3190 from Kuraray with a shore A hardness of 90A.

TPU-3 is a butanediol adipate MDI based TPU with a melt index of 10 anda shore A hardness of 80A.

EVOH-1 is a copolymer of ethylene and vinyl alcohol containing 44 mol %ethylene.

Gel content of a sample is measured according to the followingprocedure. Into a vial around 0.3 g of the sample and 10 ml THF arecharged. The sample forms a cloudy solution, which is transferred intoan ultracentrifuge tube. An additional 5 ml fresh THF is used to washthe vial and the solution/solvent is added into the centrifuge tube. Thewashing is repeated for one more time. The ultra-centrifuging conditionwas set at 18-20 krpm, 60 min, 10° C. After centrifugation, it isobserved that the gel is deposited at the bottom of the tube. The clearsolution is transferred out and the THF is removed by evaporation. Bothgel and recovered TPU are dried to a constant mass; gel content iscalculated as weight of gel divided by total weight of gel plus TPU,multiplied by 100.

Mn is the number average molecular weight and PDI is the polydispersityindex, both of which are measured in the conventional way by gelpermeation chromatography.

Example 1

Dry TPU-1 (58.91 g), EVOH-1 (3.10 g) and various amount of glycerin(GLY) was mixed in a Brabender mixing head at 195° C. at a speed of 40RPM for 40 minutes. The percent gel was determined.

Comparative Example 1 Example 1a Example 1b Sample TPU-1 + 5% TPU-1 + 5%TPU-1 + 5% EVOH-1 EVOH-1 + 0.5 EVOH-1 + 1 wt % GLY wt % GLY % Gel 34 169The gel content decreases with increasing glycerin concentration.

Example 2

A 90 wt % EVOH-1 10 wt % glycerin sample was produced by extrusion usinga Prism TSE 16 mm extruder. Liquid injection of glycerin was utilized.5% sample and 95% TPU-2 was mixed in a Brabender mixing head at 194° C.at a speed of 40 RPM for 40 minutes. A blend of 5% EVOH-1 and 95% TPU-2was produced under the same conditions for comparison. The percent gelwas determined.

Comparative Example 2 Example 2 Sample 5% EVOH-1 + 95% TPU-2 5% (90%EVOH-1/10% GLY) + 95% TPU-2 % Gel 50 36Gel content was reduced to 36% with the addition of glycerin.

Example 3

Mixtures of 5/95 EVOH-1/TPU-3 and various amount of alcohols wereextruded using a Brabender twin screen extruder. The temperaturesettings were 190, 210 and 210° C. for zone 1, zone 2 and die,respectively. The screw speed was 40 rpm. After extrusion, the blendswere dried and re-extruded to about 2.5-3.5 inch wide, 30-40 mil thicktapes on a Brabender single screw extruder at temperatures of 190, 200,200 and 200° C. for zone 1, zone 2, zone 3 and die, respectively. Thescrew speed was 40 rpm. The gel content of the tape was measured.

Alcohol % Gel Mn PDI Comparative Example 3 None 31 39,000 2.43 Example3a 0.1% glycerin 27 36,000 2.59 Example 3b 0.25% glycerin 27 40,000 2.10Example 3c 0.5% glycerin 21 40,000 1.71 Example 3d 0.14% 24 39,000 2.30trimethylolpropane (TMP) Example 3e 0.34% TMP 22 40,000 2.15 Example 3f0.68% TMP 21 35,000 2.21 Example 3g 0.16% neopentyl 27 38,000 2.61glycol (NPG) Example 3h 0.41% NPG 27 37,000 2.26 Example 3i 0.82 NPG 2135,000 1.79The gel content was reduced with the addition of alcohol. The molecularweight of the soluble portion of TPU was not largely affected by thepresence of alcohol in most cases.

Example 4

Same as Example 3 except that the low molecular weight alcohols werereplaced with 1000 molecular weight ethylene glycol adipate (EGA) orbutanediol adipate (BDA) diols from Witco.

Diol % Gel Mn PDI Example 4a 1% EGA 28 39,000 2.65 Example 4b 2% EGA 1843,000 2.44 Example 4c 4% EGA 13 53,000 1.63 Example 4d 1% BDA 25 39,0002.23 Example 4e 2% BDA 17 44,000 2.48 Example 4f 4% BDA 12 47,000 1.59

1. A shoe, comprising an upper and a sole, wherein the sole comprisesone or more inflatable membranes for containing an inflationary gas,wherein at least one of the membranes comprises a multilayer composite,wherein the composite comprises at least one flexible layer comprising alow gel sheet formed from a composition comprising a blend ofthermoplastic polyurethane, hydroxyl functional copolymer, and a gelreducing additive, wherein the composition comprises 0.05% to 20% byweight of the gel reducing additive, wherein the hydroxyl-functionalcopolymer comprises a) a polymer having 10 mole percent or more ofrepeating units of structure

wherein n is 1, R1 and R2 are independently hydrogen, methyl, or ethyl,and R3 is hydrogen or C₁₋₃ alkyl, or b) a copolymer of ethylene andvinyl alcohol with 25-60 mol % ethylene, and wherein the gel reducingadditive is selected from the group consisting of compounds with two ormore hydroxyl groups, compounds with at least one primary amino group,compounds with at least one secondary amino group, compounds with atleast one carboxyl group, and compounds with at least one carboxylicanhydride group.
 2. A shoe according to claim 1, wherein the compositefurther comprises at least one layer of ethylene vinyl alcohol copolymerand at least one layer of thermoplastic polyurethane.
 3. A shoeaccording to claim 1, wherein the composition comprises 0.5% to 20% byweight of the gel reducing additive.
 4. A shoe according to claim 1,wherein the composition comprises 1% to 20% by weight of the gelreducing additive.
 5. A shoe according to claim 1, wherein the hydroxylfunctional copolymer comprises a copolymer of ethylene and vinylalcohol.
 6. A shoe according to claim 5, wherein the molecular weight ofthe gel reducing additive is less than or equal to
 2000. 7. A shoeaccording to claim 5, wherein the molecular weight of the gel reducingadditive is less than or equal to
 200. 8. A shoe according to claim 5,wherein the gel reducing additive comprises a compound having two ormore hydroxyl groups.
 9. A shoe according to claim 5, wherein the gelreducing additive comprises a compound with two or more amino groups.10. A shoe according to claim 5, wherein the gel reducing additive isselected from the group consisting of ethylene glycol, diethyleneglycol, glycerol, trimethylolpropane, ditrimethylolpropane,pentaerythritol, ethylenediamine, diethylenetriamine,triethylenetetramine, polyethylene glycol of molecular weight less thanor equal to 400, propylene glycol, and dipropylene glycol.
 11. A shoeaccording to claim 1, wherein the composite comprises outer layers madeof a blend of thermoplastic polyurethane, ethyl vinyl alcohol copolymer,and gel reducing additive, and the inner layers comprise alternatinglayers of ethylene vinyl alcohol copolymer and thermoplasticpolyurethane.
 12. A shoe according to claim 11, wherein the compositecomprises 10 or more inner layers.
 13. A shoe according to claim 11,wherein the composite comprises 30 or more inner layers.
 14. A shoeaccording to claim 1, wherein the composition comprises 0.05% to 5% byweight of the gel reducing additive.
 15. A shoe according to claim 14,wherein the hydroxyl functional copolymer comprises a copolymer ofethylene and vinyl alcohol.
 16. A shoe according to claim 15, whereinthe composite comprises 10 or more inner layers.
 17. A shoe according toclaim 15, wherein the composite comprises 30 or more inner layers.
 18. Ashoe according to claim 15, wherein the gel reducing additive comprisesa compound having two or more hydroxyl groups.
 19. A shoe according toclaim 15, wherein the gel reducing additive comprises a compound withtwo or more amino groups.
 20. A shoe according to claim 15, wherein thegel reducing additive is selected from the group consisting of ethyleneglycol, diethylene glycol, glycerol, trimethylolpropane,ditrimethylolpropane, pentaerythritol, ethylenediamine,diethylenetriamine, triethylenetetramine, polyethylene glycol ofmolecular weight less than or equal to 400, propylene glycol, anddipropylene glycol.
 21. A shoe according to claim 14, wherein thecomposite further comprises at least one layer of ethylene vinyl alcoholcopolymer and at least one layer of thermoplastic polyurethane.
 22. Ashoe according to claim 14, wherein the composite comprises outer layersmade of a blend of thermoplastic polyurethane, ethyl vinyl alcoholcopolymer, and gel reducing additive, and the inner layers comprisealternating layers of ethylene vinyl alcohol copolymer and thermoplasticpolyurethane.